The present invention relates to cement compositions, and methods of making and using these compositions.
Cement slurries are often applied to metal structural members in order to provide a fire-resistant coating. Products in this field include gypsum-based formulations that contain gypsum as a binder, a lightweight inorganic aggregate, such as vermiculite, a fibrous substance such as cellulose, and an air-entraining agent. The slurries are generally prepared at ground level, pumped to the point of application at the constructions site, and then applied through a spray nozzle. It is also possible to add an acidic accelerating agent, via a spray nozzle, into the composition at a point just prior to application, to accelerate the setting rate of the cement slurry. If the slurry contains a basic material, such as a carbonate, it will react with the acidic accelerating agent to foam the composition. Such compositions are described, for example, in U.S. Pat. No. 4,904,503.
In order to be suitable for such use, the slurries must possess a number of important properties. They must be able to hold a relatively large quantity of water such that they are sufficiently fluid to be pumped easily and to great heights. They must retain a consistency sufficient to prevent segregation or settling of ingredients and provide an adequate volume of applied fireproofing per weight of dry mix. The coating slurries, furthermore, must adhere to construction surfaces, such as a steel surface, both in the slurried state and after setting. Also, the slurry must set without the undue expansion or shrinkage, which could result in the formation of cracks that can deter from the insulative value of the coating.
A further factor that affects the formulation of the cement compositions is set time. The slurries must not set before application, yet must set quickly enough so that multiple layers can be applied in a reasonable period of time. To this end, as noted above, a set retarder is often included in the composition, and then an accelerating agent is added just prior to application, to ensure quick setting. Desirably, the set retarder is sufficient to prevent setting for about 4 to 8 hours, while adding the accelerating agent will then cause setting within 15 minutes.
Construction of buildings usually takes many months, and depending on the size of the building, the cement slurry will be applied over the course of many days. Usually the equipment for applying these compositions, including pumping systems, hoses, reservoirs, spray nozzles, etc., must be cleaned each night to prevent the cement slurry from setting inside the equipment.